In recent years, among fields of sanitary materials using disposable absorbent articles such as disposable diapers, disposable pants, and sanitary napkins, particularly in the field of adult disposable diapers necessary for nursing care for elderly people in relation to excretion, an absorbent article having a high absorbing capacity to ensure long-time use and having a shape stability to ensure shape retainability during use is desired so as to prevent a user who wears a diaper from being awaken for changing diapers a number of times and so as to reduce the work burden on caregivers.
A conventionally available absorbent article includes an absorbent between a liquid-permeable top sheet and a liquid-impermeable back sheet. As this absorbent, there has been used an absorbent mat obtained by forming fibrillated pulp fibers, absorbent resin powder, thermoplastic fibers, or the like into a mat, and fixedly wrapping up the mat in thin paper or the like.
In order to improve the absorbing performance of such an absorbent article, there has been proposed a method for increasing the amount of the absorbent resin powder contained in the absorbent mat. However, the swelling absorbent resin powder often causes the absorbent mat to get out of shape.
Further, by increasing the amount of the fibrillated pulp fibers that form the absorbent mat, the absorbing performance of the mat can be improved. However, if the amount of the fibrillated pulp fibers in the absorbent mat is increased, the mat is thicker. As a result, the user disadvantageously feels stiff in the hip joint and feels quite uncomfortable after long-time use. In addition, if the amount of the pulp fibers is increased, a phenomenon tends to occur that a body fluid such as urine once absorbed by the mat flows back from within the mat toward the top sheet. The body fluid thus flowing back adversely influences the skin of the user. The influence is particularly serious when the user uses the absorbent article for a long time.
As an absorbent article that prevents the backflow of the body fluid, there has been proposed so far an absorbent article that includes an absorbent material having a water-absorbent layer that contains water-absorbent resin between a liquid-permeable top sheet and a liquid-impermeable leak-proof sheet (JP-A 2002-224161). According to this technique, a material composed of a water-absorbent resin and a fibrous base material is used as the absorbent material, and another water-absorbent resin layer is provided between the liquid-permeable top sheet and the surface of the absorbent material.
The water-absorbent resin layer according to the above technique is formed so that the water-absorbent resin is independently dispersed or so that the water-absorbent resin is held between the water-absorbent sheets of cellulose fibers or the like. Thus, even if the layer contributes to backflow prevention, the shape stability is not at all considered. If the water-absorbent resin powder absorbs the body fluid and swells, the high water-absorbent resin layer may possibly get out of shape.
Further, as a very thin absorbent material that does not get out of shape after absorbing water, a very thin absorbent sheet body that does not contain pulp fiber other than nonwoven fabrics and is formed so that a water-absorbent resin powder is held between two nonwoven fabrics by a web-shaped hot melt adhesive has been proposed by the applicant of the present application (WO 01/89439).
In this technique, since the water-absorbent resin powder is fixedly retained by the web-shaped hot melt adhesive, the sheet body does not get out of shape. In addition, since the sheet body is very thin, a user who wears an absorbent article using this absorbent mat as an absorbent feels quite comfortable. However, taking into consideration the long-time use of the absorbent article that employs this absorbent mat as an absorbent, it is necessary to ensure a higher absorbing capacity. In order to ensure the higher absorbing capacity, a method for providing multilayer absorbent sheet bodies to be used as the absorbent mat or for increasing an area per absorbent sheet body or an amount of the water-absorbent resin powder per absorbent sheet may be considered. However, if a number of absorbent sheet bodies are used or the amount of the water-absorbent resin powder per absorbent sheet body is increased, a ratio of the water-absorbent resin powder contained in the entire absorbent mat becomes increased. As a result, the mat disadvantageously becomes a stiff absorbent mat, which makes the user feel stiff. In addition, to increase the area per absorbent sheet body, it is required to increase an area of the disposable absorbent article itself accordingly. This is disadvantageous not only in its production but also in usability.
Moreover, the main component of the absorbent sheet body that exhibits the absorbing performance is the water-absorbent resin powder. Therefore, the absorbent sheet body is inferior in water absorption speed to a conventional absorbent mat that is composed mainly of pulp fiber.
The present invention has been completed in view of these circumstances. It is an object of the present invention to provide a disposable absorbent article including an absorbent mat that can promptly absorb a body fluid such as urine, that has a high absorbing performance enabling long-time use, that hardly gets out of shape even if absorbing a body fluid, that hardly causes backflow of the body fluid, and that can make a user who wears the article feel comfortable.